Power transmission system



July 14, 1931.

POWER TRANSMISSION SYSTEM F. w. GAY I 1,814,684

. Filed Oct. 12, 1928 Patented .luly"l4, i

L `'rperinatal: w. een or nnwzrnm Nnwf Jansma rownn'rnnnsmissron sYsrnM application una october 12, iozswsemi no. V312,085.

c This invention relates, generally,` to` the` transmission of electricI power; `and `thcin-f vention `has reference, more part1cularly, `to av novel power transmission system that 1s so Q5 constructed and arran ed as` to inherently against destruc-` protect its transmission` ines tive short c1rcu1t currents.

Heretofore, current limiting reactors have` been em loyed to limit such short Vcir-cuit curl or eilicient operation, `the t reactance c of suchfreactors-is ordinarily relativelyv low" :lo rents. l

' so asto produce a normal voltage drop ofnot more than a few PIODt. In obtainy ing such eliiciency however, the safety of the "115 system su'ersforfuponfthe occurrence of a shortlcircuit the current in the shortcircuited line may riseftomany timesnormal value-` Such Ashort c1rcu1t currents not only destroyV insulation on the line, but alsofcausevoltage 2o Vdisturbances whichlthrowl synchronous machines out of step and are generally the chief e cause of unsatisfactory service on many sys-` tems. c "f e Arlar'ge percentage of therfaults thatV de-` velop on transmisslonlinesare caused by lightning or switching surges `or otherdlstaken from service for a y orderthat repairs may be made. c 1

The protection of aftransmission system against such faults is a serious problem "for the protective system must select the faulty,

line and disconnect the same before the c am#` ageat the point of fault has become disastrous` 40 and before the continuous" operation of the system isV jeopardized` Heretoipre,` ithas been customary to obtain selectivity by vary-` f `ingsrthe reference characters 1,2 and 3 desi g1 e nate an electric power station bus that A; 1h

ing` the time setting of the relay. y. .f

is 'an `ob 'ect of` this i' ventionto provide anovel power transmission system .wherein the power currents, uponthe occurrence, of a" short circuit, are prevented from flowing into" such `short circuit buttare; compelled to con-1 tinue on the conductors through "the"` oint of'short circuit to their destination.` e ence,

the power currents jiowing in a short circuited `transmission lineoofthis invention `are the same lafteralshort circuit asbefore the 0c-` currence of the same.

It is another Object of;

this invention t to `provide suitabletmeanslfor short circuiting and grounding .transmission `lines that develop ia'ults.A j

`In lcarryn transmission1 ines are so connected through autoftransforlners tliatone half of the powerw normally liowsover eachline. A failure on;

one `of these lines immediately causes the cntirepower to flow over the remaining line at""doubleffvltage. The shortcircuiting and open icircuiting of transmission llnes `under theA'p-resentLinvention `by means of `switches out Vthe invention, ;a pair of, f f

`is easily andV cheaply accomplished since,

thatiniiist switchedi` Itis importantto; note that `modern transmission lines are in-` there .l are no, eircessive` e short circuitlcurrents ma' sulated to withstand lightning and switching l surges and are-therefore readily able to withstand double `.voltagestforV short Vperiods of tirneduring repairs and changes are beingymade on the line out of service.`

"Otherobjects of this inventionnot at this time moreparticularly enumerated, will be` clearly. understood from the following detailed description of the same. t f1 t c The'invention is clearlyillustratedrin the-4 accompanying drawings, in which i Fig. 2 isa graphic representation showing the life of` electric cables usedV in carrying out the invention, i

Similar characters of views to designate corresponding parts. e

e. Referring now" to Fig. l of the said drawadapted to supply electric energy through one c Fi l is a wiring diagram illustrating the nove power transmission system of this 1nvent1on;and

st i

`reference are em'-` `ployed` inall of the hereinabove `described or more of the novel transmission `systems of `this invention to` a substation bus 20, 2l and y 22,` `One such transmission systeme` is shown connected to the bus 1, 2 and 3 by supply leads e 4, and 6. `A circuit breaker 7 is included in vand 18 carry one half of. theenergy supplied the leads 4, 5 and Leads 4, 5 and@V are connected to the mid-tap of three single phase auto-transformers 8,9 and 10. Three conduc# tors 12, 13 and 14 lof atransmission Vcableor line`15 are connected to corresponding ends of autoftransformers 8, 9 and 10. lThree simi-Y Alar conductors 16, 17 Vand 18 of a transmission cable or Vline 19 are connected to the opposite ends of the transformers 8, 9 and 10.

Each of theconductors 12, 13,714,716, 17

by the auto-transformerS, 9" or 10; to which it are connected toterminal leads 26, 27 and 225V which are connected in turn tothe substation isconnected. This distribution-ofthe load by the auto-transformers causes cable 15 to carry `one half .of the transmittedload and Acable 19 .v the other half thereof. The cables 15 and 19 `of these cables are connected to receiving autotransformers 23, 24 and 25 that are simi-A lar to auto-transformersS, 9'and 10.Y vThe mid-taps of auto#transformers 23, 24 and 25 v bus20, 21- ,and 22; A circuitbreaker 30 isineluded inthe'circuit ofleads 26,27 and A28.

VIn, operation, the power Jcurrent flowing "frompowerstationbus-1, 2and 3 over leads 4,5 and 6 is equally `divided in each phase at the mid-points of transformers 8, 9 and 10.` One half the current in each phase passesin `one direction throughv its corresponding` transformer .andf the p through transformer in the oppositeY di-y rection. "This `results in ione half of the current `of eachphase flowing throughjconducto'rs12`, 13Mand 14V of cable 15 ,'andthey -other half of such current flowing through conductorsglb, 17 and `18 `of cable 19. Y This dividedl'phase current is again united at the substation by autotransformers 23, 24 and 25 and then delivered to substation .bus 20, 21`

and 22.4 The voltagedropbetween circuit breaker 7 and circuit breaker` 30" will be that due to the impedance of the auto-transform# ers which may be relatively low, together with that of the cables `15 and V19. f Y Y Should either of the cablesl 15 or 19 becomefshort circuited at some point offits length betweenthe power station andthe substation, thenr the;V remainingcable' willV l,carry thetotal load. This may be shown by `assuming, forlexamplalthat cable 19V is short circuit at Under such shortfvcircuit` condition`s,`the halves Vof the Vwindings offthe,

autostransformers 8, 9, 10, 23, 24 and 25 Athat are connectedfto'conductors 16,117 'and 18 remainder passes:V

ground becomefstar' connected.` "These auto-transA .formers which up to this time were unexcited and had Vpractically no magnetism inV their coresnow become excited to double voltage, causmgthe voltage in conductors Y12, 13 and 14 to double, thereby causing cable V15 to carry the entire load that was previously i carried bycables-15 and 19;v ltfi-syevident l that the currents will still^` divide at the mid points ofthe auto-transformers 4as before and willflow`tlirough conductors 16, 17 and 18. Substantially the only current that will flow from conductorto conductor at fault X-X .will bethe exciting current of the siX autotransformers. Thus, by pairing thepower cables as described above disastrous -short cable failureare avoided g l:

It willbe evident that this system'provides circuitsV which have heretofore occurred upon a means for instantly detecting'a de fectiye'f` cable. This 'will beapparent"toVv those'fskilled inl the art'l since the voltmeters commonly in#- Vstalled' in connection with power lines or cables suchfas15 and 19 willlindicate to the.V

station operatorthat line 19, for example,` is

carrying no voltag'e`, whereas line 15 .is'car ryingjtwice normal voltage, thereby showing l that a fault exists in 'linel19y lt is apparent' thatrfalseoperation oflrelays on "the systemf I will, not occur Vsince substantially the only abnormal currents produced'onthe system by the fault are the exciting currents of the auto-` negligible.`

Vtransformers which on l large systemfare` "Various Y means may l bek employed other than hand control,V for switching or cutting a cable outlof service upon theoccurrence of'a fault therein'. V' Upon the occurrence ofthe short' circuitlat X--X switches 31 and 32 are voperated either automatically or by hand to short circuit" and ground the defective cable V19. The faulty section as at Xf-X may then y be replaced vand switches 31 and 32 again operated to complete-gl the power circuit Y, through the cable 19-and resun'ie normal opelrationv thereof. "Inithe event of asimultaneous faultlonvboth :cables v15anvd 19 or `a fault ona cable anda' simultaneous transformer V failure, the circuit breakers 7 and 30 may be opened to rupture the heavyrshort circuit current flowing. lfcables and transformers are properly tested the possibility of such af Vsimultaneous failure is remote." Switches,- 33 and'34 may be used toshort circuiti and cable`l15 whena fault occursin this cable.

' If desired, the circuit breakers and may be opened upon' the'occurrence of a fault 'i and thereby prevent more than a momentary operation of-a cable at double voltage. Also,

, switchesf31` and 32 mayfirst be closed. uponj` 1 the occurrence of a failure in cable 19 and.;` then immediately opened.- ASuch operationv f will generally quench an arc ove-ran insula- 4 V tion failure and allow normal service to be- 1 20` logarithmic scale. Also, itiseomrnon knowlf edge that such cables after installation and` tion does not materiallyiai'ect'ltheflifeof" transmission cables" usedyalthough suchcaf bles mayn besnbjeetedto doublei normal volt-` ageswfor temporary periods` "In FigQZ of" the" drawings, the insulationwstress'` in volts per mill of insulation thickness-"in a cableis plottedas ordinates and timefin f hours is plotted as obscissas. Curve `A` givesthe life curve of the insulation `on` la modern three conductor high `voltage cable atno loadt It is.` well knownthat the life-curve `ofsuch cables is'a straight linelwhen `plotted to logarithmic scale against volts also plotted to under load will not withstandcontinuouslya as ozite which givesthe )oints a breakdown endurance against" surgefvoltages that is but littlenbe ter than instantaneous. `splice joints, constructedof materials simibeinginstalled having a volt-life 7 stress in a cable resulting from normal volt#` y age on such cable. Theintersection of line C` cable life after this theoretical Vreduction of voltage much more than one half that shown by laboratory test. Curve B is plotted" with ordinates of a magnitude equal to `one half of those of curve A. `In the past, the charac-4 teristics of cables havenot been clearlyun-l' ders-toed and it has been impossible to use f i such cables to theiryfullcapalcity owing to f ineilicient splice joints employedin installaF tion of the cables` `Such joints have commonly been filled with liquidcompound such lar to those used in cable construction, are

` curve approximating that of curveB. n i

Horizontal line C illustrates the `insulation with curve B gives the total life of a cable operating continuously undernormal voltafreconditio'nB i From Fi 2 itwill be seen s g i, i

that the life of Sucha cable is one million i hours.U4 "After 100,000 hours or. eleven and one-half years service,provided thecable has only been subjected to lightload, `its life should be reduced approximately ``one-tenth` as an additional factor of safety owing to the age of the cable. Curve D shows the one-tenth has been made. Curve B shows L 'that the installed cable may be expected to y have a life of 6,000 hours when subjectedto double voltage when comparatively new and 5,400 hours when subjected to double lvoltage after a previous voltage lifeof 100,000 hours or eleven and one-haltyears. Itis therefore evident that if the cable has beenoperated for a total time, of, `for example, 300 hours at double voltage during the eleven and onehalf years of` service, `then itslife hasfonly been shortened approximately five percent `hers and imaybeapened Modern ot thienormal life of such cable; l, It is con` sideredthat 300hours should be a suicient total :time for removing defects a except` ,in Cl'SeSiOflOIlgcableS' l u l It is to be understoodthat curve A `is derivedfromlaboratory tests and that actual installed i performance as rep-resented "by curve B can only be maintained by Vcarefl'il testingand elimination of cable defects as :by using direct` current at high fvoltage.

Such cable defects occur as theresult otre-v peated expansion` and contraction due tol i heating'` and cooling, especially whenfthe cable is strainedseverely owing, `for example, A,

to overheating Otan adjacent: cableI or to a heavy overload continued for several hours. Also loads maintained on cablesextending `through poorlyfcooled ductsV and man holes `are the principal cause of short cable lifeand the next most proline cause of shortened ca`` ble; life results `from short circuit currents which may be tento twenty times normal and maycontinuefor many seconds.

i As `many changescould be made in th above construction and many" apparently widely diierentembodiments of this inventionlcould bemade without departing from the scope thereof, it is intended that all mat ter contained in the :above description or shown inthe accompanying drawings shall `be interpreted as `illustrative and notina limiting sense. f a NVhat: is claimed isn;

l( Atransmission system comprising, a

Vpolyphase station `buslhaving a plurality of phaseconductors, a pair of polyphase trans- Y mission 1ines,l each having `a plurality of phase conductors,- a plurality of transformers `corresponding `in number to thenumber of phase conductorsin said bus, each of said transformers having' a continuous winding with azmid-tap connected to one of saidbus phase conductors, the ends `of each said wind ing i 2."A transmission system comprising, a polyphase station bushaving a pluralityof phase conductors, a pair of polyphase transmission lines, each having a plurality of phase conductors,apluralityiof transformers 'Y corresponding 1n" number to the number of phase conductors in said bus, `,each of said transformers having a continuous `winding with a mid-tap `connected to one of said bus phase conductors, the ends of each said windeingconnected to a Vphase conductor of each oi: said transmission lines.

y .no

lngbeing connectedto a phase conductor of each ofsaid transmission lines, said thusly connected transmission line phase conductors being of the same phase as the bus conductor i connected to the winding mid-tap.`

`3. A transmission` system comprising, a v polyphaselsending bus and a polyphaserecelving bus, said busses having aplurality of phase conductors, a pair of polyphase transmission lines, each,A having" a pluralityfof `said transformer windings having their 1nid` taps connected toseparatel phase conductors ofsaid sending'pbusand others of said trans Y former windings having their mid-taps con?.

` conductors'of saidtransinission lines iso that nected toseparatefphase conductors `of saidl `receivingbus, the ends rof saidtransfornier windingsbeing connected to separate Vphase the busV conductor and transmission line conductors connected to any one transformer `Winding are all of the same phase. Y

f 4V; A transmission system comprising, aV

' polyphase; sending bus and a polyphase ree fY ceiving bus, said busses having Va plurality'of phase conductors, a' pair of polyphase transmission lines, each having a plurality of phase conductors, aplurality of transformers, `each of said transformers having a continuous winding with a mid-tap, certain ,of

said transformer windings having their mid-V taps connected to separate phase conductors of said winding bus and others of said transe` former windings having their mid-taps confV nected to separate phase conductors of said receiving bus', the headsrof said transformer windings being connected to separate phase conductorsof said ,transmission lines so that eachpair of transmission line conductors in` Y the same phase but indifferent lines are connected through a transformerwinding at eachend ofthe transmissionlines to a bus conductorof the same phase as their own.

5.V A transmission system comprising, `a polyphase station bus having a plurality of` Aphase conductors, a pair of polypliase trans- ,iniziati rbusV and output transformers each of. said output transformers having two connected winding sections interlinkedbyVV a- Vcommon core, the connected endsofsaid winding sections being connected to a.. respective .phase offsaidoutput bus, the otherv end of each of said `connected winding sections: being connected to thecorrespondingphase lead of a respectiveone of said transmission lines, said winding section of said 'sending'fstation and receiving station transformers operatingzto maintain the normallimpedance path for power currents during a tiinejof fault on one of said transmission lines.

Y In testimony, that I claim the invention set forth above I have hereunto set my hand this v 10th day of October, 1928. v Y -FRAZER Wi GAY.

mission lines, each having.` aplurality of l phase conductors",` a plurality of transformers corresponding in number to thejnumber of phase conductors in said bus, each of said transformers having a continuous `winding with a mid-tap connected to one of said bus phase conductors, the ends of each said wind- Y ing'being; connected to a phase conductor of each of said transmission lines, and means for grounding either one or the other vof said transmission linesasdesired. v QQ Y f6. In a transmission system, in `combination, an electric power'sendinggstation, an electric power receiving station,y two three e phase transmission lines arranged to convey three phase `power from said sending station Vto said receiving station, said sending station f having an input bus andinput transformers,

Y each ofsaid transformers having two con# nected, winding sections interlinkedby a common core, the connected ends ofsaid sro 'winding sections being'connected to a respec I tivephase of said input bus, the other end of each of saidjeonnected windingsections being connected to the' corresponding phase lead of a .respective one of said transmission lines,` said receiving station having an output' los in) Y 

